| Code: O-14 |
| Abstract: 317 |
| Bispecific antibody constructs mediate specific retargeting towards and elimination of HBV-positive hepatocytes and tumor cells |
| Bohne F.M.1, Hasreiter J.1, Quitt O.1, Bockmann J.-H.1, Momburg F.2, Protzer U.1 |
| 1Helmholtz Centre Munich / Institute of Virology, Munich, Germany, 2DKFZ / National Tumor Centre, Heidelberg, Germany |
| Background & Aim: Chronic hepatitis B is characterized by exhausted effector cells, incapable of eradicating the virus. To circumvent this limitation, HBV-specific retargeting of immune effector cells using bispecific monoclonal antibody (BiMab) constructs is a promising therapeutic approach. In this study, effector cells are supplied with BiMab that redirect T cells towards HBV infected cells and activate their cytotoxic potential. Methods: We constructed tetravalent BiMab harboring two single chain fragment (scFv) binding domains. The first scFv targets the small HBV-envelope protein (HBs) on the plasma membrane of infected hepatocytes. The second binding motif engages T cells via CD3 and co-stimulates them via CD28. The two binding moieties are connected through an IgG1-derived Fc-domain and dimerize through disulfide bonding in the hinge region. This results in tetravalent homodimers comprising two scFv-binders for the target antigen and two for effector cell recruitment. Results: In co-culture experiments, the redirection of and immune effector cells towards HBs-positive hepatoma cells by the BiMab induced specific elimination of target cells and activation of effector cells. Co-administration of HBs/CD3- and HBs/CD28-specific BiMab constructs resulted in synergistic and mediated up to 96% specific elimination of HBs-positive target cells in co-cultures with PBMC. Interestingly, also singly administered BiMab were capable of inducing T-cell activation. Sorted CD4+ T cells displayed superior cytotoxicity in comparison to CD8+ T cells. The isolated subpopulations of naïve, central and effector memory T cells hinted at CD8+ naïve T cells to be incapable of BiMab-mediated killing. Intracellular cytokine staining showed polyfunctional activation mediated by the biMab, resulting in simultaneous secretion of IFNγ, IL-2 and TNFα. Importantly, biMab were also able to redirect T cells to HBV-infected HepaRG cell resulting in specific killing. Furthermore, soluble HBs, mimicking the high viral loads in patient serum failed to induce effector cell activation even when added to non-infected cells. Finally, first in vivo experiments in immunodeficient mice transplanted with HBV-positive hepatoma cells to induce subdermal tumors showed that transferred human PBMC mediated a marked decrease in tumor size upon BiMab injection indicating a functional homing in tumors. Conclusion: Retargeting of T cells towards HBV-positive target cells using bispecific antibody constructs is a promising new immunotherapeutic approach to treat chronic hepatitis B and associated hepatocellular carcinoma. |
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